There are many instances in water and wastewater treatment when two very common contaminants, for example, (1) organics and (2) hardness, are removed to render the water usable for purposes of drinking, irrigation or other reuse applications, or for use in industrial processes.
The removal of organics (often collectively referred to as “Total Organic Carbon” or “TOC”) is important in drinking water treatment because some organic constituents combine with chlorine used in water disinfection to form harmful and sometimes carcinogenic compounds. For this reason, TOC removal is important and strictly regulated in drinking water treatment. In other water and wastewater treatment applications, removal of organics is also important for varying reasons. Some common reasons are related to the ability of many organic compounds to foul downstream treatment processes (such as membrane processes) or industrial equipment (such as cooling tower packings, boilers and the like).
Removal of hardness (calcium and magnesium) is generally important because the presence of excessive levels of hardness can cause aesthetic problems for drinking water and also increases the potential for scaling and post-precipitation, which can be very harmful to pipes, downstream processes and industrial equipment.
These two common contaminants (organics and hardness) are simultaneously found at excessive levels in many water sources. Many drinking water sources (surface waters) contain high levels of both organics and hardness depending on the geographic location of the surface water (for example, such waters are commonly found in Florida in the United States). Increasingly, municipal and industrial wastewater effluents are being reused or recycled for purpose of irrigation or industrial process use. These waters often contain elevated levels of organics and hardness which may need reduction prior to the reuse application.
The removal of these two contaminants, when present simultaneously, has long been a challenge in the treatment of water and wastewater. The reason that the simultaneous removal of these two contaminants is very challenging is complex from a chemistry perspective. The physical-chemical removal of these two contaminants (organics and hardness) from water or wastewater can be very difficult because of the antagonistic conditions under which each removal process is accomplished or optimized. The most common approach for the removal of organics and hardness in waters which contain the two contaminants simultaneously has been either (1) two-stage clarification: a physical-chemical precipitation/adsorption process or (2) nanofiltration: a membrane process which incorporates a very small porosity fiber to separate a significant amount of hardness and organics via a physical barrier dependent upon molecular size exclusion.
With regard to the first alternative for simultaneous reduction of organics and hardness, physical-chemical precipitation, it would be clearly advantageous if there were some means to accomplish the chemically antagonistic goals of organics removal and softening within the same vehicle or process, without the necessity of a two-state process. This invention solves that problem by substantially improving the process and cost efficiency in accomplishing the desired reduction of both contaminants.